1. Field of the Invention
This invention relates to the field of analog and digital displays. More particularly, this invention provides a method and apparatus for reducing flicker when displaying processed digital data on video displays having a low refresh rate.
2. Background
It is sometimes necessary to display digital video information on interlaced video displays having refresh rates below 60 Hz. In these cases, if an image is improperly filtered, as is common in graphics originating on personal computers, the display image will flicker. Visual perception of this flicker increases as the contrast between adjacent lines increases. Thus, it is often necessary that images be processed in order to reduce the flicker.
Digital video information is typically organized as pixels, the smallest piece of digital video information. Although each pixel in an image is a fixed number of bits, depending on the color depth of the information, the number of bits each pixel requires may vary. For instance, a pixel may be 8 bits wide (one byte), as when defining any one of 256 shades of gray (from complete black to complete white), 15 or 16 bits wide (covering 256 different colors of 256 different intensities), or may be 24 bits wide (one byte for each color component red, green, and blue, thus allowing for millions of colors).
Digital information is typically stored in a rectangular array of memory locations, but may be stored in any format, depending on the circumstances. For the convenience of discussion, it is assumed here that the digital display data to be processed is stored in a rectangular memory array having a width equal to the number of bytes a display line is wide, and a height equal to the number of vertical display lines.
Typical prior art systems which display digital data on low refresh rate video displays retrieve the data from memory one display line at a time, storing the data in an external line buffer having enough memory to store several lines of display data. Following any desired processing, the resulting video data is then provided to an National Television Standards Committee (NTSC) or Phase Alternating Line (PAL) encoder to generate a composite video signal which is then displayed.
Although the prior art process described above is useful for its intended purposes, the storage of several lines of digital video data and any subsequent processing takes place in an external line buffer.
Another disadvantage of prior art systems is that large amounts of valuable memory space is required to store and process several lines of data at a time.